Electronic devices often incorporate several semiconductor devices that communicate with one another over channels. High-speed operation is often a design parameter of such devices, requiring the bandwidth of the channels to be used efficiently. Current-mode drivers and voltage-mode drivers are often incorporated into transceivers to facilitate high-speed communications. Current-mode drivers and voltage-mode drivers may drive differential signals across the channel, but such drivers can consume considerable power.
Current-mode drivers utilize one or more current sources. Current-mode drivers may be undesirable in various applications because the current sources used in such drivers consume power to drive the outputs. Further, terminations at both the driver and a receiver are generally used for impedance matching, which decreases the equivalent resistance seen by the driver's output and thereby increases current consumption.
As an alternative, voltage-mode drivers may be used to drive signals. In contrast to current-mode drivers, voltage mode drivers consume less current for a particular voltage swing. However, these drivers typically use an additional voltage supply, because the output voltage swing of the driver is constrained by the supply voltage. In addition, implementation of the additional voltage supply may involve use of a large capacitor or a voltage regulator that may be difficult to incorporate onto a semiconductor die using standard fabrication procedures. Also, selective equalization of a signal to be transmitted, i.e., using a limited amount of power to drive the signal, can be difficult to implement using voltage-mode drivers.